This invention relates to a synthetic resin lens and, more particularly, to a synthetic resin lens having a surface hard coating.
A synthetic resin lens, especially a diethylene glycol bis(allylcarbonate) resin lens, has excellent safety, machinability and fashionableness when compared with glass lens, and has become popular at a rapid rate in keeping with evolution of hard coat techniques, and anti-reflection techniques. As eyeglass lenses are recently produced from plastic materials, there is an increasing demand for thin type plastic lenses formed of a high refractive index resin material. The refractive index of diethyleneglycol bis (allylcarbonate) resin is 1.50, and some proposals have been made for obviating the deficiency. For example, Japanese Laid-open Patent Publication No. 41965/1979 discloses an example of a copolymer of diethyleneglycol bis(allylcarbonate) and benxylmethacrylate, Japanes Laid-open Patent Publication No. 77686/1979 discloses an example of a copolymer of diethyleneglycol bis (allylcarbonate) with 4-iodostyrene and Japanese Laid-open Patent Publication No. 15513/1983 discloses an example of a copolymer of diallylisophthalate or diallylterephthalate with a methylmethacrylate prepolymer. In these cases, problems are presented in connection with lens manufacture in that the allyl groups are reacted with (metha)acrylic or vinyl groups different in reactivity from the allyl groups. That is, the (metha)acrylic or vinyl groups having a higher reaction rate are polymerized first and the allyl groups having a lower reaction rate are polymerized subsequently such that not only the desired copolymerization is not achieved, but the allyl compounds are not polymerized completely, with the result that the solvent resistance is lowered.
As other examples, Japanese Laid-open Patent Publication No.13747/1980 shows an example of a copolymer of bisphenol A dimethacrylate with phenylmethacrylate or benzylmethacrylate, while Japanese Laid-open Patent Publication No.54901/1982 and Japanese Laid open Patent Publication No.18602/1983 show an example of a copolymer of a styrene base monomer with di(metha)acrylate having a halogen-substituted aromatic ring and an allyl compound or di(metha)acrylate. In these cases, although the (metha)acrylic groups and the vinyl groups have similar reactivities to each other, certain difficulties are presented in supervising the process of lens manufacture. That is, because of the higher reaction rate, the casting conditions are difficult to control such that distortions may be caused in the interior and on the surface of the lens with resulting optical defects. In addition, the vinyl or (metha)acrylic groups are highly sensitive with respect to the reaction and may be easily affected by external conditions such that the reaction can be controlled only with extreme difficulties except by changing the polymerization conditions. The result is that the process becomes necessarily complicated because of the difficulties in the polymerization reaction and in view of satisfactorily completing the polymerization reaction. Also, when the monofunctional monomers are employed as a main component in the above prior-art examples, since it is impossible for the monomers to be completely polymerized and incorporated into the polymer chain, it may occur that the heat- and solvent resistance of the copolymer may be occasionally affected by the unreacted monomers.
These manufacture difficulties may be obviated to some extent in a further example, namely a copolymer of a diallyl compound having a halogen-substituted aromatic ring with diallylterephthalate or diallylorthophthalate. In the present example, since the reaction is rather easy to control, and since all the monomers are bifunctional, the process including mixing of the solutions and the polymerization of the solutions can be supervised rather easily, so that a high refractive index synthetic resin lens may be obtained with good optical qualities. However, because of the higher specific gravity of the diallyl compound having the halogen-substituted aromatic ring as the main component, which is as high as about 1.7 as the polymer, the lens is increased in weight such that the merit of the high refractive index lens is lost. Also, the diallyl compound having the halogen-substituted aromatic ring does not lend itself to the purpose of mass production since the costs in the synthesis and purification thereof are higher than in the case of ethyleneglycol bis (allylcarbonate) or other synthetic resins for lenses, even when taking into account the merit of the high refractive index proper to such a compound.
The problem common to bisphenol A dimethacrylate, di(metha)acrylate or the diallyl compound having the halogen-substituted aromatic ring employed in the above examples is the high susceptibility of the monomers being precipitated. In many cases, these monomers are dissolved in monomers with which they are copolymerized. However, the contents of the monomers are limited because the monomers tend to be precipitated easily even at room temperature when dissolved in more than a predetermined amount. Since it is necessary to maintain the temperature higher than a predetermined temperature, and polymerization initiators must be selected from a narrow range of materials, the manufacture process is difficult to control, starting from mixing to polymerization of the solutions.
For overcoming the aforementioned inconveniences, there is also proposed an example of a copolymer of a diester of fumaric acid having an aromatic ring with an acrylic compound or an allyl compound. However, since the proposed copolymer is inferior to the composition of the present invention with respect to the polymerization degree, it cannot exhibit sufficient properties with respect to durability, such as solvent- and impact resistance under hostile conditions.